H-NS mediated compaction of DNA visualised by atomic force microscopy

The Escherichia coli H-NS protein is a nucleoid-associated protein involved in gene regulation and DNA compaction. To get more insight into the mechan ism:of DNA compaction we applied atomic force microscopy (AFM) to study the structure of H-NS-DNA complexes. On circular DNA molecules two different l evels of H-NS induced condensation were observed. H-MS:induced lateral cond ensation of large regions of the:plasmid. In addition, large globular struc tures were identified that incorporated a considerable amount of DNA. The f ormation of these globular structures appeared not to be dependent on any S pecific sequence, On the basis of the AFM images, a model for global conden sation of the chromosomal DNA by H-NS is proposed.